Point of No Return, self explanatory I would say.
I wouldn't.
The PNR as correctly defined by KW is the last point at which you can still make a choice to continue or go back.
Beyond the PNR you cannot return.
IMHO a pedant might say the term should be
Last
Point of
Return!
As currently labelled it's therefore
not 'self-explanatory' and a bit misleading.